These notes provide very wonderful words that should be googled, and sites that should be checked out.
1) Structure: wesabe.com uses sticky tags, uses tags as part of the resources, bubble-up type, semantic tags – ex. ia (information architecture), Zigtag.com mined Wikipedia
2) Leveraging communities: LibraryThing – user-driven vocabulary to combine or separate tags
3) Automanual Folksonomies: mixed approach at Etsy (like eBay for handmade items, unique items), LibraryThing tagmash – like set math with Union and Intersection, “semantics on top of minimal structure”
4) Pace Layers: speeds of innovation from nature level up, starts with Mr. Brand, moved into IA by Peter Morville, (faceted tags)
5) Sparking innovation: Flickr, Dan Catt, geotagging